MOSFET (metal oxide semiconductor field effect transistor) H-drives have been known heretofore. For example, Ray Ruble in an article entitled "The MPP 500" on pages 14, 19 and 20 of Powerconversion International of July/August 1984 shows in FIG. 2a a Low Voltage Fast Bridge wherein each upper FET is driven from the drain of the lower FET and shutoff is accomplished with one pullup resistor for each upper FET. For reactive loads, to avoid reverse conduction through the intrinsic diodes or dv/dt effects during switching which could damage the P-channel MOSFETs, at input voltages below forty volts, Schottky diodes in parallel with the MOSFET intrinsic diodes are sufficient, since the forward drop of the Schottky diodes is less than the intrinsic diode drop. At higher voltages, that is, thirty to ninety volts, more complex arrays using blocking diodes and conducting diodes as shown in The High Voltage Fast Bridge of FIG. 2b of the above publication have been required. Also, as shown in said FIG. 2b, capacitive coupling for the gates of the upper FETs has been used and functions by using the input capacitance of the upper FET as half of a capacitive voltage divider which divides the voltage change in the drain of the lower FET to a level appropriate for gate drive on the upper FET. In this arrangement, P-channel and N-channel MOSFETs with equal input capacitances are used.
While these systems have been useful for their intended purpose, they have been handicapped by being limited in voltage applications to ninety volts or less. Also, the capacitive coupling slows down or limits the operating speed of the system. It also limits how long it can be turned on (the duty cycle) because the capacitor will charge and then after a time interval it shuts itself off. Also, it has additional power dissipation when turned on due to the forward voltage drops of the two blocking diodes VSK320 that are forward biased. Moreover, this prior MOSFET system that uses capacitive coupling is not likely to function properly on an AC system because the capacitor will conduct current all of the time. Moreover, the number of components including the four conducting diodes IN6080 and the four blocking diodes VSK320 is large.
It has been found desirable to provide an AC/DC power MOSFET reversing H-drive system that overcomes the above disadvantages.